Automated wire bonding processes, particularly thermosonic wire bonding processes, have long been a popular and reliable way to connect semiconductor dies to packing terminals by way of a wire loop. Wire bonding processes are considered to be one of the most cost-effective and reliable ways to form interconnects within semiconductor systems. Conventional wire bonding processes include ball bonding and wedge bonding attachment motifs. Ball bonding methods apply energy to a wire, such as through brief exposure to an electric arc, to form a liquefied ball of metal (referred to in the art as a free air ball) upon the tip of the wire, which is then contacted with a bonding pad with further ultrasonic agitation to form a metallurgical bond. Wedge bonding methods differ in their application of energy to the sidewall of a wire to facilitate formation of a metallurgical bond. Undesirable pad splash, pad cratering, and damage to an underlying electronic component can sometimes occur in conventional wire bonding processes if they are not performed carefully.
Gold has traditionally been used as a wire material in wire bonding processes, particularly ball bonding processes, due to various operational advantages. Recent increases in the price of gold and accompanying price volatility have led to a search for alternative wire materials, with copper being an often-utilized choice in some applications. A chief advantage of copper compared to gold is the much lower cost of copper. Inductance and capacitance are also similar for these two metals. Copper, however, has other physical and metallurgical properties that differ significantly from those of gold. The differing properties of copper lead to competing advantages and disadvantages when utilizing this material in wire bonding processes. Copper can desirably be utilized at smaller wire diameters and provide higher electrical performance (i.e., lower parasitic resistance), improved thermal behavior, and greater mechanical strength (i.e., increased hardness) compared to gold. However, in order to overcome the greater hardness of copper, a higher energy input can be needed in conventional copper wire bonding processes to facilitate formation of a metallurgical bond. The higher energy input can result in an increased incidence of pad splash, pad cratering, interface spreading, and electronic component damage. Increased susceptibility of copper to oxidation and corrosion can also be problematic. These combined effects can be associated with an increased incidence of device failure, lower processing reliability, and limited throughput (yield). Indeed, the wire bonding community has implemented strict processing parameters for conventional copper wire bonding processes to reduce the risk of bonding pad damage. These rigorous processing parameters can be very difficult to maintain and can severely limit throughput. An additional difficulty associated with conventional copper wire bonding processes is the higher pitch sometimes produced with this metal compared to gold, which correspondingly decreases the attainable wire density upon a bonding pad or other surface. Although copper has the potential to provide performance that is at least comparable to that of gold, the foregoing limitations of conventional copper wire bonding processes presently limit use of this metal to various low-end consumer products.
In addition to the strict processing parameters typically utilized during conventional copper wire bonding processes, the hardness of this metal can also significantly increase wear within a wire bonding system in which it is used. Specifically, a capillary bonding head providing a copper wire payout can wear much faster than when a gold wire is provided. The increased system wear associated with copper can result in significant cost increases, particularly for high-volume applications, due to process downtime and material costs of replacing broken parts. Although more robust capillary bonding heads are in development, failure of this component still remains an issue in conventional copper wire bonding processes. Despite recent advances in dispensation technology, accelerated grain growth within the free air ball and low pullout forces can remain problematic in conventional copper wire bonding processes.
In view of the foregoing, improved systems and methods to facilitate wire bonding, particularly copper wire bonding systems and methods, would be of significant interest in the art. The present disclosure satisfies these needs and provides related advantages as well.